1. Field of the Invention
The present invention relates to a structure of a projection for an electromagnetic pick-up in a rotor, comprising a detecting projection provided on one side of a rotor, such as a pulley, for generating a rotation detecting pulse in an electromagnetic pick-up disposed in proximity to the one side.
2. Description of Related Art
A pulley having a pulley body which is integrally provided with detecting projections of the above-described type for the electromagnetic pick-up for the purpose of reducing the number of parts and the number of assembling steps is conventionally known. For example, Japanese Patent Application Laid-open No. 62-96860 describes such a pulley.
It is conventionally known that in producing a pulley body integrally provided with detecting projections of the above-described type for the electromagnetic pick-up in the above manner, the pulley body may be formed from a sintered material. In this case, the projection is formed simultaneously with the formation of the sintered material from a green compact.
It is also known that a pulley body may be formed by casting and after this formation, a projection of the above-described type is formed by cutting.
Further, it is known that a pulley body may be formed by pressing a plate material. In this case, a projection of the above-described type is merely formed into a protrusion-shape by a forming die.
However, when the pulley body is formed from the sintered material, as described above, it is difficult to produce a larger pulley body because of production equipment.
In addition, when the pulley body is formed by casting, and after this formation, the projection is formed by cutting, high working accuracy is required, resulting in increased cost due to the large amount of time required and difficulty associated with mass production.
Further, when the pulley body is formed by pressing the plate material, there is an advantage that a relatively large pulley body can be mass-produced inexpensively. However, the projection is merely formed to bulge into a protrusion shape upon the pressing, having a poor accuracy in size. Moreover, the formed projection assumes a gentle or rounded profile. For this reason, when the projection is detected by the electromagnetic pick-up, a pulse cannot be outputted sharply. If the output pulse has a gentle profile, when noise is generated and superimposed on such an output pulse, there is a possibility that a control unit (such as an ECU), which operates in response to the pulse, may misjudge the signal.